Always the assumption of supports. I don't like to make this comparison, but act the same like it's a black guy having money or something of worth in the Jim Crow era (or hell, even this era).
"He has something good, there's no way he could have LEGITIMATELY obtained this. He must have stolen it!"
And then people wonder why no one wants to be the support.
EDIT: Actually, let me better illustrate this. One game, I was Karma support. I get ambushed in mid as we're pushing it by three of the enemy team. Our Zed is basically right next to me, but he's out of the fight and dancing on the outside of it, waiting for me to wear down the enemy and die before he can swoop in and claim all the kills. The thing is, that never happens. I somehow ended up getting a triple kill despite being the only combatant in that fight. He realizes this and tries to come in at the last second, but doesn't even get an assist on half of them. He then rages at me in the all chat for the rest of the game that I stole the kills from him, even when the enemy team wasn't the slightest bit interested in him, AND he made an effort to stay out of the fight until he realized that I was going to win it.
And then people wonder why no one wants to be the support.